In encapsulating a component in a matrix, the matrix material is generally heated to a sufficiently high temperature to provide a plasticized mass which facilitates coating of the component. Upon cooling, the matrix material hardens or becomes solidified and protects the encapsulant from undesirable or premature reaction. However, heating of the matrix to plasticize it or to form a melt may deleteriously affect or decompose the encapsulant as well as the matrix material. Additionally, the mixing or high shear used to disperse the encapsulant uniformly throughout the plasticized matrix material may likewise adversely affect the matrix material or encapsulant. Furthermore, the use of high temperatures to plasticize or melt the matrix material may cause evaporation and loss of the encapsulant. The addition of liquids to the matrix material to reduce its viscosity and to facilitate mixing may require excessive drying or evaporation of the plasticizing liquid for the attainment of a formable composition capable of being formed into discrete, substantially uniform pieces. Furthermore, removal of the plasticizing liquid may adversely expand the product, decrease its density, and make the encapsulated component more susceptible to attack or more easily released.
The production of expanded products is disclosed in European patent publication nos. EP 0465364 A1 (published Jan. 8, 1992) and EP 0462012 A2 (published Dec. 18, 1991), U.S. Pat. No. 3,962,416 to Katzen and U.S. Pat. No. 3,786,123 to Katzen. The two European patent publications disclose the production of an anti-obesity food and a method for making it by extrusion of starches with fatty acids into an expanded product having densities between 0.1 and 0.3 g/cm.sup.3. U.S. Pat. No. 3,962,416 to Katzen discloses an expanded product which contains at least one nutrient and one gelatinized starch.
U.S. Pat. No. 3,786,123 to Katzen discloses a method for producing encapsulated nutrients using extrusion temperatures of between 250.degree. F. and 400.degree. F. and extrusion pressures of between 200 psi to 2500 psi. A high protein encapsulating agent containing up to 40% starch may be used. The starch is gelatinized and extruded into an expanded product.
However, in producing a product having controlled release or delayed release, excessive expansion or puffmg may result in too rapid release properties or may undersirably expose an encapsulant to destructive reactions. For example, an edible composition for delivering encapsulated pharmaceutically or nutritionally active components or for a non-edible agricultural product for delivering biocides or herbicides, it is desirable that the products have a substantially spherical shape and a high density. Such products exhibit a substantially low ratio between surface area and volume and thus minimize or prevent surface related destructive reactions that occur upon exposure to air or oxygen and light. The spherical shapes and high densities also minimize the surface which would be available to expose embedded material which is not encapsulated. Furthermore, for edible products for delivering pharmaceutically or nutritionally active components, it is desirable that the products are capable of being consumed or swallowed without chewing or substantially no chewing. Avoiding the need for mastication, further assures that the products reach the digestive tract without substantial enzymatic hydrolysis in the mouth. Furthermore, it helps to control or reduce dissolution of the product in gastric juice and to control the release of the embedded or encapsulated components in the stomach and/or in the intestine.
International patent publication no. WO 92/00130 (published Jan. 9, 1992) discloses a continuous process for obtaining an encapsulated, biologically active product in a starchy matrix. A biologically active agent and starch are mixed before extrusion and extruded as a blend, with the encapsulant or biologically active agent being heated together with the starch. Altematively, a core material to be encapsulated may be added and blended with an aqueous dispersion of starch after the starch and water have been subjected to an elevated temperature sufficient to gelatinize the starch. The extrusion process, it is disclosed, exposes the mix to high shear mechanical action at a temperature above the gelatinization temperature of the starch. The use of extrusion barrel temperatures of between about 58.degree. C. and 98.degree. C. are disclosed. While these barrel temperatures may be above the gelatinization temperature of starch, the extruder utilized has barrel sections that are only three 1 l/d long. The screw speeds utilized, between 400 rpm and 200 rpm, result in a very short residence time of the blend inside the extruder and barely allow heating up of the starch water mix. As a result, the temperatures obtained are generally too low to obtain substantial gelatinization of native starches. Additionally, the barrel temperatures used are particularly too low for substantial gelatinization of high amylose starch which generally gelatinizes at temperatures substantially above 100.degree. C., for example at 125.degree. C. The use of extrusion barrel temperatures which are not sufficiently high to substantially or completely gelatinize the starch may not form a sufficiently continuous, plasticized and homogeneous matrix for effective embedding or encapsulation.
In addition, the use of relatively low extrusion temperatures, high speed mixing, and a high viscosity starch composition generally requires a high mechanical energy input. High shear is directly related to high specific mechanical energy, which in turn increases the molecular destructurization and dextinization of starch. Breakdown of the starch molecules, and in particular the amylopectin, increases the solubility of the extruded starch composition in aqueous systems as described in P. Colonna, et al., "Extrusion Cooking of Starch & Starchy Products," Extrusion Cooking, C. Mercier, et al. pp. 247-319, AACC, St. Paul, Minn. (1989) and F. Meuser, et al, "A Systems Analytical Approach To Extrusion," Food Extrusion Science & Technology, ed. J. Kokini, Dekker Publ., pp. 619-630 (1992). Increased solubility of the extruded starch in aqueous systems decreases the stability of the product against moisture and subsequently diminishes or shortens the protection and controlled release of the embedded or encapsulated substances. In addition, subjecting the encapsulant to the same high shear and high temperature conditions to which the starch is subjected may adversely affect the encapsulant by at least partially destroying it or decomposing it into unknown solid or volatile substances.
Pregelatinized starch is used in numerous applications in the food industry as a swelling agent and for accelerated and extended water absorption in foods such as soups, sauces, instant puddings, baby food, and thickening agents. However, it has been found that the use of pregelatinized starch or the use of starch as the only matrix material during extrusion cooking generally results in a matrix which releases the encapsulant too quickly. It has been found that the penetration of water into a pure starch matrix causes early release of the encapsulant into the environment. Generally the time to release 100% of the encapsulant is too short to provide a desirable time-release or controlled-release which is effective for delivering the encapsulant at a desired location or time.
International patent publication no. WO 95/26752 (published Oct. 12, 1995) discloses the production of a food product for the enteric supply of a fatty acid, a fatty acid containing substance, an amino acid, or an amino acid containing substance by at least partially complexing the fatty acid or amino acid in the amylose helix of starch to mask the acid. The product may contain one or more flavors and colors, fat soluble substances, anti-oxidants, or pharmacologically effective substances. The components may be first dry mixed and subsequently fed into an extruder where they are substantially mixed and subsequently heated above the gelatinization temperature of the starch to obtain an elasticized mass which is extruded and formed into pellets. However, heat-sensitive components would be destroyed during the heating step.
International patent publication no. WO 85/04074 to Flashinski, et al. (published Sep. 26, 1985) discloses an insect bait containing an insect-controlling material in a gelatinized starch matrix. The bait is made by coextruding starch with the insect-controlling material at temperature and pressure conditions sufficient to cook and gelatinize the starch. Alternatively, a pregelatinized starch may be mixed with the insect-controlling material and water to form a gel. In the formation of the insect bait by mixing and extruding the components, it is disclosed, it is essential to utilize additives, including the insecticides and repellants which will withstand the extrusion temperatures of starch without the degradation or vaporization. The extrusion temperatures of the insect-bait mixture, depending upon the starch content and other additives, ranges between about 160 to about 310.degree. F. at pressures of from about 300 through 800 psi.
U.S. Pat. No. 5,183,690 to Carr, et al. discloses a continuous process for imparting predetermined release properties to an encapsulated biologically active agent in a matrix of starchy material. The starchy material, an active agent, and water are continuously blended in an ingredient stream wherein the starchy material is at a solids concentration of at least 40%. The ingredients stream is continuously extruded as an extrudate and the extrudate is continuously recovered. The conditions of blending, extruding, and recovering are preselected to yield the predetermined release properties. The temperature is elevated to at least about 65.degree. C. to effect gelatinization of starch and assure an essentially molecular dispersion of the starch in the water. Alternatively, the core material to be encapsulated is added and blended with the aqueous dispersion of starch after the starch and water has been subjected to an elevated temperature sufficient to gelatinize the starch. In this embodiment the aqueous starch stream containing gelatinized starch may be lowered to a temperature as low as about 25.degree. C. before the core material to be encapsulated is added and subjected to high-shear mechanical action. Under such low temperature conditions of admixture it is disclosed, the activity of sensitive biological material, such as bacteria and viruses, is preserved and loss of volatile organic materials is minimized. The rate of swelling of the products in water and the rate of release of active agents are controlled by altering the amount of water present in the starch-agent-water blend during processing. As the amount of water is decreased, both the swelling rate and the release rate increase. The rate of swelling of the products in water and the rate of release of active agent are also controlled by passage of the extrudate containing starch-agent-water through an exit die of various dimensions. As the exit die is reduced in size, both the rate and extent of swelling increase and the rate of release of agent increases.
The present invention provides a controlled release particulate composition which contains a hydrophobic component for controlling the release of an encapsulated and/or embedded active component from a plasticized matrix. High water binding capacity agents may also be used to delay or control the release of the encapsulant from the matrix. Furthermore, in the process of the present invention the amount of plasticizer is high to facilitate plasticization of the matrix material at low shear and is then reduced prior to adding the encapsulant to facilitate subsequent forming and to reduce post extrusion drying. The controlled release or delayed release composition may be produced without substantial expansion of the matrix material to thereby avoid production of a low density product which prematurely or too rapidly releases the encapsulant or the embedded component. The products may be produced using low shear mixing to avoid decomposition of the matrix material and encapsulant or active component. However, even though low shear mixing is utilized, substantial plasticization of the matrix material and at least substantially uniform distribution of the active component are achieved. Edible products produced in accordance with the present invention for delivering pharmaceutically or nutritionally active components may be consumed or swallowed without chewing so that the products may reach the digestive tract without substantial enzymatic hydrolysis in the mouth. In addition, in embodiments of the invention, the substantially spherical shape and high density of the products reduce or prevent substantial surface related destruction of the active components upon exposure of the particles to air, oxygen, light, or water. Timing of the release of the embedded or encapsulated component so that it is delayed until the product reaches the stomach and/or the intestine may be controlled by the use of varying amounts and types of hydrophobic components or high water holding capacity components in the plasticized matrix. The processes of the present invention may be used for the continuous production of an edible composition for delivering pharmaceutically or nutritionally active components, or for the production of an agricultural product for the controlled release of biocides, herbicides, fertilizers, growth stimulators, pesticides, or products for other uses such as, for example, detergents which release chemical and/or biological agents.